clear; clc;
syms kesi yita
N1=1/6*(1+yita);
N2=-1/6*(1+yita);
N3=-1/6*(1-yita);
N4=1/6*(1-yita);

M1=1/2*(1+kesi);
M2=1/2*(1-kesi);
M3=-1/2*(1-kesi);
M4=-1/2*(1+kesi);
B=[N1,0,N2,0,N3,0,N4,0;
      0,M1,0,M2,0,M3,0,M4;
      M1,N1,M2,N2,M3,N3,M4,N4]
D=[1,0,0;
       0,1,0;
       0,0,1/2]
B.'
M=B.'*D*B
int(int(M,kesi,-1,1),yita,-1,1)*3/4